Which statements are true? Explain why or why not.

$10-1$ It is estimated that about $30\%$ of the proteins encoded in an animal's genome are membrane proteins that are required for a cell to function and interact with its environment.

$10-2$ All of the common phospholipids$-$phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and sphingomyelin$-$carry a positively charged moiety on their head group, but none carry a net positive charge.

$10-3$ Although phospholipid molecules are free to diffuse in the plane of the bilayer, they cannot flip$-$flop across the bilayer unless enzyme catalysts called phospholipid translocators are present in the membrane.

$10-4$ Whereas all the carbohydrate in the plasma membrane faces outward on the external surface of the cell, all the carbohydrate on internal membranes faces toward the cytosol.

$10-5$ Although membrane domains with different protein compositions are well known, there are at present no examples of membrane domains that differ in lipid composition.